I've recently purchased a Mac in order to get some experience developing for a third platform, in addition to Windows and Linux. To start with I'm simply trying to port a couple of my existing programs, and a question has come up that I can't seem to find a solution to. In the past, I've been able to have certain parts of my code only compile for certain OSes by using #ifdef commands. For example:

#ifdef _WIN32
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nCmdShow){
#else
int main(){
#endif

However, I've been unable to identify an equivalent condition that can be used for identifying Mac OS X. This presents difficulties as a result of a few differences, like the fact the OpenGL headers are in a different path, OpenGL, instead of GL. I'd like to be able to do something like:

#ifdef _MAC_OS
#include <OpenGL/gl.h>
#else
#include <GL/gl.h>
#endif

It's occurred to me because of its UNIX heritage it may not actually be possible, in which case I'd most likely have to turn to a tool like autoconf or something instead. Still, I'd appreciate any advice that would let me keep my source consistent and compiling regardless of the platform.

You could always add your own _MAC_OS define for the mac version (in the commandline of the compiler for example), if all else fails. :)

There's definitely a define for it built in, I can't remember what it is though (I, too, recently bought a mac). I'll see if I can't look it up and let you know.

Thank you, all of you!

I forgot to reply to the AP, so I'll do that now: It works fine. Taking it on a more single-step basis, apparently __APPLE__ is the define that's working best for me, for some reason __MACOSX__ doesn't seem to be present, even though SiCrane's link claims it should be. Oh well, as long as one of them works.